the average human has two arms and two feet, and can be described as “dibrachius dipus”. conjoined twins can be joined ventrally (joined facing each other) or laterally (joined side by side).
i have made a chart of conjoined types (click to see in full size)
two arms – dibrachius
three arms – tribrachius
four arms – tetrabrachius
two heads – dicephalus
joined at the:
face – cephalopagus
head – craniopagus
brain, head & chest – epholothoracopagus
chest (side by side) – thoracopagus
trunk (front or back) – omphalopagus
xiphoid region – xiphopagous
lower body (side by side) – parapagus
hip – ischiopagus
Illac (abdominal area near pelvis) – iliopagus
rear end – pygopagus
next step: to sketch out a set of illustrations of each conjoined type